Some of the city’s ritziest hotels are beefing up security in the wake of a brazen weekend jewelry heist at the Four Seasons in Midtown.

The Plaza and Intercontinental are adding guards and updating their security cameras after a trio of bling-hungry crooks made off with two pricey watches and a diamond pendant from a Jacob & Co. display window at the Four Seasons at around 2 a.m. Saturday.

With a getaway driver idling outside, the other two robbers smashed the glass with a hammer, snatched a handful of baubles and took off, sources said. Hotel security sources have told The Post that most of the surveillance cameras in the area weren’t functional and that they suspected an inside job.

Jacob “Jacob the Jeweler’’ Arabov, who owns Jacob & Co., told The Post yesterday that the crooks “left the hammer behind with their fingerprints on it.”

The jeweler to the stars said the bungling thieves dropped a $20,000 Epic watch on their way out.

A hotel source valued the sparkling haul at $2 million, but Arabov insisted that he had lost only roughly $75,000 worthy of merchandise.

The diamond merchant said the case contained $750,000 worth of jewelry and that the hammer attack only broke through a small portion of the glass.